The Effect of Isabgol (Plantago psyllium) Mucilage and Shiraz Thyme Essential Oils on Microbial Load and Improving Shelf Life of Fresh-Cut Carrot

Fresh-cut produce graduated to retail during the1990s, especially for lettuce, cabbage, carrots and other similar vegetables. The high microbial loads of these products after harvest can be substantially reduced through a cleaning in flowing chlorinated water and adistribution under ensured controlledrefrigeration. Therefore, a good number of convenient ready-to-use greens were launched to the market in the past decade. Nowadays, theuse of this technology to achieve similar results in fruit products is one of the most challengingtargets for processors. However, there is anumber of issues that still need to beovercomebeforefresh-cut fruit commodities can be sparked off to anoutstanding position in the segment of lightly-treatedrefrigerated foods. The importance of freshly cut products increases day by day. Tissue and cell rupture leads to a decrease in the shelf life of these products. On the other hand, these products due to increased enzyme activity, respiration rate and microbiological considerations that affect the health of these productsrequires highly attention.To increase the shelf life of the products and prevent undesirable changes in cut slices of fruit or vegetables a coating on the surface of these products has been suggested. Mucilages and essential oils of herbs are natural compounds that can be used to create such covers. The advantages of these coatings are their bactericidal effect, maintenanceof pleasant taste and other physical and chemical characteristics of the product and even decrease of environmental pollution. In this research, the effect of natural compounds such as Zataria multiflora essential oil (EO) and Plantagopsyllium mucilage on storage life and microbial load of fresh cut carrot was studied.
The research was conducted in two separate experiments on fresh-cut carrot: In the first experiment, the effect of different concentrations of Plantago psyllium mucilage (0,100, 200, and 400mgL-1) and four concentrations of Zataria multiflora essential oil (0,100, 250,and 500 mgL-1), in a factorial experiment on the basis of completely randomized designwith16treatments and three replications was evaluated. In the second experiment application of essential oil and mucilage on microbial load of fresh-cut carrot was examined in a split plot experiment on the basis of randomized complete blocks design with six treatments and three replications which Zataria multiflora EO (500 mgL-1) and Plantago psyllium mucilage (400 mgL-1) was set as main plot and storage time was set as subplot. The serial dilution technique and cultivation in special culture media were used to determine the microbial load. Treated samples were then packaged in polyethylene trays (175mL) and were stored at 4°C. After10 days of treatment different parameters such as weight loss, total soluble solids (TSS), titratable acidity (TA), pH, color, organoleptic properties, the amount of skin whitening and microbial load were evaluated.Means were compared using LSD test at the significant 5% probability level.
The results showed that the treatments had a significant effect on weight loss. Essential oil and mucilage treated samples with different concentrations and also a combination of the two had less weight loss than the control. Different concentrations of essential oil and mucilage individually significantly affected titra table acidity, soluble solids and pH. Samples treated with 100 and 250 mgL-1essential oil, and with 100 and 200 mgL-1 mucilage had the highest acidity, and showed significant increase compared to the control. A little color changes occurred in the treated samples and their colors were very close to the control. Combination treatment with 100 mg.L-1essentialoil plus 100 mgL-1mucilagesignificantlyreduced skin whitening of fresh cut carrot. Analysis of variance indicates significant effect of treatments on all microbial contaminations which were evaluated. The means of aerobic mesophilic bacterial contamination and the coliform bacterial contamination were 6.67 log CFU/g and6.37 log CFU/g, respectively. Only mold and yeast contamination significantly increased during storage and was more pronounced in samples treated with psylliummucilage. After 10 days of storage, although some bacterial contamination increased, this increase was not significant. Fungal contamination starts at 5.35 log CFU/g and endsat 6.64 log CFU/g, which is approximately 1.3 log CFU/g increased. E. coli contamination was not observed in samples.According to the standards threshold, in this experiment, aerobic mesophilic bacteria contamination of the samples (except for samples coated with mucilage after 10 days of storage which their contamination exceeded) was in the standard threshold.However, coliform bacteria, mold and yeast contamination in all samples exceeded.
In general, results of this study showed that application of natural compounds of medicinal plants as edible coatings improved the quality and -extend the shelf life of fresh cut carrot. .However, disinfection of the product in this experiment was not sufficient to reduce the microbial contamination properly and treatments used could not reduce it at the standard limits, appropriate disinfection methods such as radiation and higher concentrations are also investigated in order to export this recommended product